RESOURCES

Arsenic Relative Bioavailability Study

The Department of Toxic Substances Control (DTSC) has been awarded a Training Research and Technical Assistance Grant to conduct an Arsenic Relative Bioavailability Study (Study) by the United States Environmental Protection Agency Region IX (USEPA). The goal of the Study is to determine the range of arsenic bioavailability that may exist in contaminated soil at former abandoned mine land (AML) sites and develop better methods to determine the human health effects caused by exposure to arsenic at these sites.

Arsenic is the key chemical of concern at the majority of Brownfield projects at former gold mines in the California Mother Lode. Through implementing the Study DTSC hopes to provide better tools for characterizing AML sites so that bioavailability of arsenic can be employed in risk assessment and risk management decisions, resulting in more cost-effective cleanups.

Currently, toxicity criteria for estimating health effects of arsenic are based on humans exposed to arsenic dissolved in water. However, arsenic at AML sites is bound to soil and rock. To properly describe arsenic risks at AML sites the site-specific relative bioavailability (RBA), which is defined as the ratio of uptake of soil-bound arsenic to arsenic dissolved in water (a ratio of the arsenic that is absorbed in the body from the soil ingestion versus that portion that would be absorbed in the body from water ingestion) must be determined. Currently, the techniques for estimating bioavailability of arsenic are expensive and time-consuming. Animal studies (in vivo bioavailability) could be conducted at each site, but the costs would be prohibitive. The Study will focus on how to predict bioavailability from inexpensive, routine measurements (in vitro bioavailability).

The USEPA grant was awarded in late 2008 and runs for 5 years, terminating in 2013. The current Study is limited to AML sites in the Nevada County area due to budget constraints. If Study results are positive, DTSC intends to expand the geographical area and produce an arsenic bioavailability guidance document that will assist in the proper characterization of arsenic at former AML sites throughout the state, however further activities beyond those planned for this Study will be necessary to achieve this.

CURRENT ACTIVITIES

Ohio State University, Chapman University, United States Geological Survey, and DTSC are performing various analyses on the samples from Sampling Event 1.

COMPLETED ACTIVITIES

DTSC prepared a Field Sampling Plan, Quality Assurance Project Plan, and a Site-specific Health and Safety Plan to allow for the proposed collection of soil and rock samples at the Empire Mine State Historic Park, located in Grass Valley, Nevada County, California.

Sampling Event 1 was conducted from September 21st through 23rd 2009. Twenty-five samples, weighing ~2600lbs, were collected according to the procedures in the approved QAPP. Samples were stored in a secure facility and shipped to the Ohio State University for processing in early January 2010.Summary of Field Activities for Sampling Event 1

Sampling Event 1 samples were homogenized, sieved and split for distribution to all investigators participating in the Study by the Ohio State University. The homogeneity evaluation included taking a total of 24 subsamples from each homogenized sample and testing each subsample for total arsenic using USEPA Method 3051a. This was a time-consuming process and splits were distributed to the investigators in October 2010.

*Photos by Dawn Busalacchi, Ohio State University

Presentations

Presentation entitled “Identifying Predictors for Bioavailability of Arsenic in Soil at Mining Sites” was made by Drs. Valerie Mitchell and John Christopher at the 2010 Society of Toxicology conference in Salt Lake City, Utah on March 10, 2010. They discussed the goals of the Study, progress to date, challenges for the Study and answered questions from attendees. The presentation was made in the Risk Assessment: Methodological Challenges and Metals session at the conference.